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Motion and Energy
Kinetic and Potential
Energy is the most central concept
underlying all science.
Without energy, nothing happens!
Energy is the
ability to cause a
change or do work.
Energy is measured
in joules (J)
Two classifications of energy
Kinetic energy
Potential energy
Potential energy  energy stored
(has the potential to do something, but is NOT doing it!)
Three types of potential energy
Gravitational potential energy
Elastic potential energy
Chemical potential energy
Gravitational Potential Energy
(GPE)
Potential energy due to an object’s
position above the Earth’s surface
– This will be because the object has the
potential to move down because of gravity!
GPE continued
The higher up an object is from the
surface, the more GPE it has.
It takes more energy to move the object to
that position, so there is more energy
stored.
Calculating GPE
A big object has more potential than a
smaller one so MASS is factored in.
The higher something is, the longer it can
fall, so HEIGHT is a factor.
GRAVITY causes the object to accelerate,
so it is a factor.
GPE = mass x acceleration due
to gravity
(9.8 m/s2)
GPE = mgh
x
height
What is the potential
energy of a 0.4 kg
ball sitting on a 1.9 m
countertop?
GPE = mgh
GPE =
(0.4 kg)
x (9.8 m/s2)
x (1.9 m)
GPE = 7.5 joules
If all of the balls have
the same mass,
which has the
greatest GPE?
WHY?
Elastic potential energy
Potential energy due to the
compression or stretching of the
object
Chemical potential energy
Potential energy found within the
bonds of molecules
Chemical potential energy
Energy in the Human body
Potential energy is stored
in the form of chemicals
such as sugars, proteins,
and fat.
This energy comes from
food.
In order to be healthy, the
amount of energy coming
in (eaten) must EQUAL the
amount of energy going
out (used during
activities).
Energy in food is measured in Calories
(*these are actually kilocalories, notice the
capital ‘C’*)
1 Calorie = 4184 Joules
It takes 1 calorie (small c) of energy to
raise the temperature of 1 gram of H2O
one degree Celsius
1 gram of carbohydrate = 4 Calories
1 gram of protein = 4 Calories
1 gram of fat = 9 Calories
Kinetic energy  energy of
movement
When an object moves, it
possesses kinetic energy. There are
fivetypes of kinetic energy radiant, thermal, sound, electrical
(light) and mechanical (motion).
Calculating Kinetic Energy (KE)
Kinetic energy is very similar to
momentum.
Since an object must be in motion in
order to have kinetic energy, VELOCITY
is a factor. (It is THE MOST IMPORTANT factor)
A large object in motion will have more
energy than a smaller object going the
same speed, so MASS will be a factor.
KE = ½ x mass
KE = ½ mv2
x
velocity2
If a motorcycle which has a mass of
200 kg is moving at a speed of 15
m/s, what is its kinetic energy?
KE = ½ mv2
KE = ½ X 200 kg x (15 m/s)2
KE = ½ x 200 kg x 225 m/s
KE = 22500 Joules
Which would have more kinetic
energy, a 0.01 kg bullet traveling
1200 m/s, or a 500 kg truck
traveling 5 m/s?
The bullet
KE = ½
mv2
KE = ½ (0.01 kg)
x
(1200 m/s)2
KE = 7200 Joules
The truck
KE = ½ mv2
KE = ½ (500 kg)
x (5 m/s)2
KE = 6250 Joules
Law of Conservation of Energy
Energy cannot be created or destroyed.
Energy changes form, but is never lost. It may
become a form that we cannot use or
recognize right away, but it still exists!!
This means that the TOTAL amount of energy
in the universe remains constant.
Example: heat from friction
GPE to KE
GPE to KE
The total amount of energy in the
system remains constant
This total amount of energy is called
the mechanical energy.
Mechanical energy = KE + GPE
Conservation of Energy
Conservation of
Energy
Elastic PE to KE
Elastic PE to KE
Elastic PE to KE
Chemical PE to KE
Chemical potential to kinetic energy
Chemical PE to KE
Chemical PE to KE
Potential to kinetic energy and
beyond
Potential to kinetic energy and
beyond
Potential to kinetic energy and
beyond
Motion and Energy video